3 Answers
3

The external portion of the nose is a little deceptive. Two nostrils
appear to lead almost straight up into the nasal passageway. In
reality, the nasal cavity, which connects the nose to the throat,
leads almost straight back. Its ceiling is approximately even with the
top of the nose, just below the eyes. Its floor tends to be almost
level with the alar cartilage, which forms the openings for the
nostrils.

As you can see in this image, there's plenty of space, but there might be some need to "wiggle" the spike in and then push up the nostrils a bit.

The skill is called the Human Blockhead. ("Skill", not "trick", because the nail is real and does go into the head.)

Here's a video of another guy inserting a 4-inch nail into his nose in a similar way.

It involves inserting the nail into the nasal cavity, and relies of people not understanding the anatomy of the skull for its impressiveness. This How Stuff Works article goes in detail about where to stick the nail.

It is a very common stunt. I am not exaggerating when I say I have seen this performed over 50 times. I'm quite over it.
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Oddthinking♦Jan 15 '12 at 0:31

1

I remember seeing Jim Rose do it back in 1991 or 1992 and tried it myself. Scarily easy to do. But you have to fight a worrying urge to sneeze, as I don't think that would be good!
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Rory AlsopJan 17 '12 at 11:28